The present invention relates to a disk device, and more specifically to a disk device having a larger control range in number of revolutions of a disk.
A conventional disk device can be, for example, a CD-ROM reading device and the like.
As shown in FIG. 4, the CD-ROM reading device is used as a peripheral device of a computer, receives an instruction from an external device (for example, a host computer 16) through an interface circuit 15 having a CD-ROM signaling circuit, searches for a target position, reads target data from the data stored in a disk 1, and transfers it to an external device. A CD (compact disk) and a CD-ROM disk is to be read at the velocity of a CLV (constant linear velocity).
However, a CD-ROM reading device as a peripheral device of a computer is firmly requested to realize a high-velocity search and a constant high-velocity read without increasing the cost. To satisfy the request, a CD-ROM disk is read four times, eight times, etc. as fast as the CLV in a constant high-velocity reading process. However, to increase the search velocity in the constant high-velocity reading process performed at four times, eight times, etc. as high as the CLV, the load of a disk motor becomes very large, and a costly and large disk motor is required.
Therefore, a device capable of reading at a CAV (constant angular velocity) a disk storing data at a CLV, and a wide range CLV system capable of performing a high-velocity search in a very wide read range in the CLV reading process, and performing a constant high velocity reading process have been recently realized. These device and system have realized a high-velocity searching process using an inexpensive and small motor with the load of a disk motor considerably reduced.
A reading system of the conventional CD-ROM reading device is configured as shown in FIG. 4. A signal read from the disk 1 by an optical pickup 5 is provided for an RF (high frequency) amplifier 7. The RF amplifier 7 extracts a high-frequency signal corresponding to the data of a disk from the output of the optical pickup 5, a focus error signal, and a tracking error signal, and provides them for a signaling circuit 8.
The signaling circuit 8 generates focus tracking control signals 11 for servo focus and servo tracking, and an EFM (eight to fourteen modulation) signal obtained by binarizing an RF signal. A focus tracking control circuit 4 controls a focus tracking coil 6 comprising a focus coil and a tracking coil according to the focus tracking control signal 11, and reads the information in the disk 1 using the optical pickup 5.
The signaling circuit 8 is provided with a phase lock loop circuit (PLL circuit) for generating a PLL clock synchronous with the EFM signal to read the EFM signal. The generation signal frequency for a phase lock loop is based on 4.3218 MHz for the CLV control, and the variable range is xc2x1several tens %. In the CAV control, the signaling circuit 8 computes a revolution velocity detection signal 9 from a spindle motor control circuit 3, and a spindle motor control signal 10 is provided for the spindle motor control circuit 3 such that the disk 1 can be revolved at the CAV. The CLV/CAV can be switched by a system control circuit 13. When a disk is read at the CLV, the spindle motor control signal 10 obtained by computing the RF signal by the signaling circuit 8 is provided for the spindle motor control circuit 3.
Since the revolution velocity detection signal 9 is constantly output with the RF signal missing if the disk 1 revolves, it is used to confirm the revolution velocity of the disk 1. The signaling circuit 8 monitors the revolution velocity detection signal 9, and can confirm the revolution state of the disk 1 in the off-focus or off-tracking state. Therefore, even in the off-servo-focus state or the off-servo-tracking state, the disk 1 can be prevented from abnormally revolving or stopping.
However, in the conventional disk device, the output width ranges of a control signal and a spindle motor control signal for servo focus and servo tracking are set such that the disk device can be safely controlled when the motor which revolves the disk is revolving at the highest velocity. For example, at a 32-time high velocity, the number of revolutions of the disk is 7,000 rpm. On the other hand, in the case of low-velocity revolutions at a normal velocity, the number of revolutions of the disk is a minimum of 200 rpm. That is, the highest velocity is 35 times as fast as the lowest velocity. Therefore, the control signal during the low-velocity revolution indicates a poor S/N ratio, thereby causing a problem of unstable control.
Practically, with a decreasing revolution velocity, the output level of the spindle motor control signal 10 and the focus tracking control signal 11 becomes lower as shown in FIG. 5(a). When the waveform shown in FIG. 5(a) is enlarged, it proves that the waveform changes in the form of a staircase as shown in FIG. 5(b). Since the spindle motor control signal 10 and the focus tracking control signal 11 are digital signals, they change in the form of, for example, a 256-step staircase.
As shown in FIG. 5(b), when the disk 1 is read with the number of revolutions of A in the range of the low velocity of, for example, 200 rpm to 500 rpm, it is desired that the output levels of the spindle motor control signal 10 and the focus tracking control signal 11 are the levels at which no staircase-shaped waveforms appear as shown by B in FIG. 5(b). However, since the output level of the control signal shows a staircase-shaped waveform by a digital signal, it actually indicates B1 shown in FIG. 5(b), thereby causing the control error of C1 which is the difference between B and B1. The control error C1 is quantization noise, which indicates a relatively large value during the low-velocity revolution as compared with the high-velocity revolution. That is, during the low-velocity revolution, the S/N ratio is low, and the revolution control or the focus tracking control of a disk becomes unstable.
The present invention aims at providing a disk device for controlling the revolution of a disk, and the operation of a focus coil and a tracking coil with high precision even during the low-velocity revolution of a disk.
The disk device of the present invention includes a control signal gain switch means for switching depending on the operation state and outputting a gain of at least one of a digital control signal output to the first control unit for controlling a motor which revolves a disk, and a digital control signal output to the second control unit for controlling reading means for reading information in the disk and outputting a high frequency signal.
According to the present invention, during the low-velocity revolution of a disk, the revolution of a disk, and the operation of a focus coil and a tracking coil can be controlled with high precision.
The first embodiment of the disk device according to the present invention includes a first control unit for controlling a motor for revolving a disk; a second control unit for controlling reading means for reading the information in the disk, and outputting a high frequency signal; signaling means for generating a digital control signal for controlling the operation of the motor and the reading means according to the high frequency signal; and control signal gain switch means for switching and outputting a gain of at least one of a digital control signal output to the first control unit and a digital control signal output to the second control unit based on an operation state. During the low velocity disk revolution, a digital control signal can be output with high precision, and the revolution of a disk, and the operations of a focus coil and a tracking coil can be controlled with high precision.
The disk device according to the second embodiment of the present invention controls a disk motor based on the detection result of the revolution velocity detection means of a disk. That is, the device is configured using the signaling means for generating a digital control signal for controlling the revolution velocity of a motor based on the detection result of the revolution velocity detection means.
The disk device according to the third embodiment of the present invention corresponds to a system obtained by combining the CLV control according to the first embodiment of the present invention with the CAV control according to the second embodiment of the present invention. That is, the device is configured using signaling means for generating a digital control signal for controlling the operation of the reading means according to a high frequency signal, and for controlling the revolution velocity of a motor by selectively switching either according to a high frequency signal or based on the detection result of the revolution velocity detection means.
Furthermore, the disk device according to the present invention is configured such that the control signal gain switch means can switch a gain depending on the number of revolutions of a disk. During the low velocity disk revolution, a digital control signal can be output with high precision, and the revolution of a disk, and the operations of a focus coil and a tracking coil can be controlled with high precision. Even when the revolution velocity is reduced due to a scratch, a spot, etc. on a disk, the gain of a digital control signal can be switched depending on the revolution velocity.
In addition, the disk device according to the present invention can be controlled in the method of changing the gain of an analog signal when a control signal is an analog output. That is, the digital control signal from the first or second control unit is an analog signal output through a D/A converter circuit, and the control signal gain switch means changes the output level of an analog signal.
Furthermore, the disk device of the present invention uses the method of changing the peak value of a rectangular wave when a control signal is a PWM (pulse width modulation) output. That is, the first control unit or the second control unit is a digital servo controller, and a control signal from one of these control units is a PWM output for control using a variable width of a rectangular wave having a constant peak value. The control signal gain switch means performs PAM (pulse amplitude modulation) control for changing the peak value of an output pulse. As in the case of an analog output, a lower price device can be realized because the D/A converter circuit can be omitted from the signaling circuit, and a power-saving and low-heating disk device can be provided with a disk revolving at a high velocity, and with the smallest electric loss when the disk is driven by a motor driver if a spindle motor driver corresponding to the PWM and PAM control can be used.